Spirochetes are motile bacteria that have periplasmic flagella rather than exoflagella. The behavioral repertoire of spirochetal cells includes coordinated swimming, reversals of swimming direction and flexing movements. In addition at least some spirochetes can "crawl" on solid surfaces. The research proposed here will employ the free-living, facultatively anaerobic spirochete, Spirochaeta aurantia, as a model in experiments aimed at an understanding of the mechanisms of motility and chemotaxis in spirochetes. Previous studies demonstrate that unlike other bacteria examined, the membrane potential of S. auranita is involved in chemotaxis. This is most likely related to the peculiar problems of flagellar motor coordination in S. aurantia. In the proposed research, the motile behavior of S. aurantia and S. aurantia motility mutants will be carefully analyzed and the effects of both spatial and temporal gradients of attractants on motile behavior will be investigated. In concurrent research, the components of the motility system will be studied at both the biochemical and genetic level. This research should provide a basis for understanding the aspects of behavior related to membrane potential and enable assignments relating other components of the motility system to aspects of behavior. This line of research should provide a better knowledge of mechanisms of chemosensory transduction and motor coordination in prokaryotes. These studies have and should continue to provide information concerning the relationship of the unique spirochetal motility system to the success of these bacteria in specific types of natural environments (mucosa, brush border of intestine, etc.).